Magneto hydrodynamic fluid accelerator and compressor



May 1, 1965 .H. HURWITZ, JR., ETAL 3,183,403

MAGNETO HYDRODYNAMIC FLUID ACCELERATOR AND COMPRESSOR Filed 001'. 6. 1960 Fig. 2. fle sfrzmvoek In vent'or's: Henry Hur'wfi'z c/lf /'-/ar' IQMKQen/"g,

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United States Patent F 3,183,403 MAGNETO HYDRODYNAMIC FLUID ACCELER- ATOR AND CGMPRESSOR Henry Hurwitz, In, and Harold R. Koenig, Schenectady,

N.Y., assignors to General Electric Company, a corporation of New York Filed Oct. 6, 1960, Ser. No. 60,995 Claims. (Cl. 315-111) This invention relates to methods and apparatus for accelerating and/or compressing a fluid. More particularly, this invention relates to a method and apparatus for accelerating and/ or compressing an ionized fluid.

In the past, techniques for accelerating and compressing fluidshave included a variety of methods and apparatus, most of which include a mechanical means for imparting a force to the fluid. In more recent times, the importance of imparting forces to gaseous fluids has been emphasized; and, in an endeavor to overcome the complexities of accelerating and compressing gases through mechanical means, ionizing techniques have been utilized. The science dealing with ionized gases or plasmain a magnetic field is generally referred to as magnetohydrodynamics (abbreviated MHD). By ionizing the gaseous fluid, new properties are imparted to the fluid which properties may be utilized to cause acceleration and/or compression in the fluid Without the need of mechanical media such as pumps, fans, etc. The application of the principles of magnetohydrodynamics to the acceleration or compression of a plasma has been attended with practical difficulties and a generally poor overall efliciency. As used herein the term compression is meant to connote raising the static pressure of a fluid, which may or may not result in an increase in density.

Attempts have been made to magnetohydrodynamically impart forces to a gas by establishing a magnetic field transverse to an electric field. In a patent to Karlovitz et al., No. 2,210,918, a device was proposed for generating electrical power through the interaction of an ionized gas with a magnetic field transverse to an electric field. It was also suggested in that patent, that the process of generation be reversed, and the generator utilized as a fluid accelerator. The application of a longitudinal electric field causes a current flow transverse to the electric and magnetic fields. This current, by interacting with the magnetic field may be used to accelerate the fluid. In such devices as shown in the previously mentioned Karlovitz patent, the longitudinal electric'current which also flows causes toroidal fluid currents which become nearly impossible to control, and thereby yield a very erratic and undependable accelerating force to the plasma. Additionally, as set forth in the copending application of Cobine and Harris, Serial No. 60,994, filed concurrently herewith, now Patent 3,149,247, granted September 15, 1964, and assigned to the same assignee, the annular geometry is not practical for operation at high temperatures due to cooling difiiculties associated particularly with the central core.

Accordingly, it is an object of the present invention to provide a method and apparatus for accelerating and compressing an ionized fluid. v a It is a further object of the present invention to provide a method and apparatus for dependably and efficiently imparting an accelerating or compressing force to a plasma.

It is a further object of the invention to provide a plasma accelerator and compressor having improvedefficiency.

It is still another object of the invention to provide a method and apparatus for accelerating and compressing a plasma Without the utilization of moving parts.

' Briefly stated, in accordance with one aspect of the in- 3,183,403 Patented -May- 11, 1965 ice vention, a channel is provided for the flow of an ionized gas therethrough. A magnetic field is established transverse to the flow of the ionized gas. Electrodes are provided at either end of the channel and are in contact with the gas entering and leaving the channel respectively. An electric potential is applied between the electrodes thus establishing an electric field along the longitudinal axis of the channel. The interaction of the electric field with the ionized gas establishes an electric current with a transverse component which impresses a force upon the gas in the direction of the applied electric field when a suitable external circuit is provided to facilitate this transverse electric current. A plasma accelerator-compressor is thereby provided which eliminates the need for moving parts or mechanical contact with the working fluid. With appropriate choice of channel size and shape, the plasma may be compressed as well as, or'instead of, accelerated.

The invention, both as to its organization and operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a'simplified plasma accelerator-compressor constructed in accordance with the teachings of the invention; and I FIG. 2 shows a system for generating electrical power including the plasma acceleration-compressor of the invention.

In FIG. 1, a simplified plasma accelerator-compressor incorporating the teachings of the invention is shown. A channel 1 having a top 2 and bottom 3,-of insulating material is provided with a plurality of electrodes 4-.7 along the sides of the channel The electrodes 4-7 are electrically insulated by insulating spacers 10 which thereby separate theelectrodesin the axial direction. Each of the electrodes 47 is electrically connected by an ideally resistanceless conductor to a corresponding electrode positioned across the channel; that is, electrode 4 is connected by conductor 11'to electrode '12 positioned across the channel 1 from the electrode 4 so as to allow a transverse current-to flow through the fluid in the channel. Accordingly, the remaining electrodes 5, 6 and 7 are connected to corresponding electrodes across the channel by conductors 14, 15 and 16 respectively. A source of electric potential 17: is connected to the electrodes posi-.

tioned at the ends of the channel. In the embodiment shown in FIG. 1, the positive terminal of the source of electric potential 17 is connected to electrode 4 by con-' ductorlS, and the negative terminal of the source of electric potential 17 is connected to the electrode 7 through conductor 19. In one embodiment it may even be desirable to'include a voltage source'in these connecting paths so as to reinforce the transverse current flow. In this instance it is possible to omit the external sourceof longitudinal voltage since, with transverse potential sources, the longitudinal field will develop spontaneously. It will be appreciated, however, that the presence of the longitudinal voltage source adds great flexibility and is highly advantageous. A magnetic field having lines of flux in the direction of thearrow 21 is established by any convenient means (not shown). The direction of plasma flow is indicated in FIG. 1 by the arrow 23.

, The-operation of the device shown in FIG. 1 may be force on the ions is transmitted to the plasma through ion-neutral collisions. The resulting effect of this electrostatic force on the ions of the plasma is the propulsion of the plasma through the channel in the direction of the electric field. The electrostatic force on the electrons tends to accelerate the electrons in a direction opposite the direction of plasma flow; however, the transverse magnetic field existing in the channel retards this reverse flow of electrons, and the low mass of the electrons minimizes the effect of the reverse electron flow on the plasma acceleration. e

The interaction of the electric and magnetic fields causes the electrons to migrate in a direction transverse to these fields, therebytending to produce an electric current transverse to the fluid flow direction. Respective opposite electrode pairs are connected through an external circuit having substantially no resistance, or a voltage source poled to aid current flow, thus providing a completed current path so that this transverse electric current does flow through the plasma and through the external circuit. This current flow results in a Lorentz force which is approximately equal and opposite to the electro-. static force on the electrons; The electrostatic force on the ions is' equal and opposite to the electrostatic force on the electrons and therefore equal to the Lorentz force on the electrons. However, the force transmitted to the gas via the ions is also approximately equal to the Lorentz force on the electrons. 'Itis this force that imparts motion to the plasma. 7

1 More precisely, if a gas is considered as moving with a velocity v in the directionof the arrow 23 of FIG. 1, through a magnetic field of strength 3 gauss in the direction of arrow 21 with an electric fieldof strength E elcc: trostatic units in the direction of arrow 23, the electric field in the transverse direction (transverse to the direction of plasma flow and tothe direction of magnet flux) :is zero because of the low resistance, or short circuiting, path provided by the electrodes in the wall of the channel in The force, F on the plasmain the X direction per unit volume arises from the Y component of the current density and is equal to t Therefore, under the approximations which have been made 7 F =neE Equation 5 may be interpreted as meaning that the electrostatic force on the ions is transmitted to the plasmaas a whole, Whereas in the high an limit the electrostatic force on the electrons is substantially compensated by the magnetic force on the electrons arising from their drift motion in the Y direction. For convenience of description, the foregoing explanation has been made upon the assumption of high m". It will be appreciated, however, that the operation of the invention is not strictly limited by this condition. Rather, in this respect, it is sufiicient if wr is not very small as compared with'unity. I It may be noted that, although the plasma has been considered as having been ionized prior to entering the accelerator channel, the plasma could easily be a gas which subsequently becomes ionized as it enters the channel through the action of electron collisions of the electrons combination with the conductors electrically connecting diametric electrodes. The formulae for the current density in the direction of the arrovg 23 '(axial or longitudinal migrating upstream. To provide this ionizing etfect within the channel, the potential applied between the entrance and exit electrodes need be raised to a sutficently high potential to cause enough electron collisions of sufficient direction) which we may designate the X direction, and

the transverse current density which we may call the Y. direction, in a partially ionized plasma are:

Here, e is the absolute value of the charge .on the electron "'inelectrosatic units, m is the mass of electron in grams,

7: is the number of electrons per cubic centimeter, .w is the electron angular cyclotron frequency, 0 is the velocity of light, and 1- is the mean time between collisions of'electrons and the moving gas atoms. This'formula assumes that theions are much heavierthan the electrons and do not" slip with respect to the moving gas. If it is assumed that an is large compared to unity(i.e. the magnetic field is strong), and the following inequalities are also assumed;

corvB Further,

maybe neglected in Equation 2 since this. quantity is energy level to'cause partial ionization of the gas. Alterjnati-vely,.the value of the voltage sourcesin the external transverse current paths can be high enough to insure breakdown. Also, one or more keep-alive discharges may be utilized. 7 I

The inherent stability of the plasmaaccelerator-com- .pressor of this invention makes it particularly suitable'for manypractical applications. The simple cross-sectional geometry facilitates proper fluid flow design and external electrical connections between electrodes providefor controllability of the transverse electron current. V.

The geometry of the plasma accelerator-compressor of 'FIG. 1 may be altered to. provide a channel having an operatively equivalent cross-section to the rectangular cross-section shown in FIG. 1. For example, an elliptical cross-section may be utilized. In any event, the magnetic field will be substantially as illustrated in FIG. 1, although slight modifications may be made for optimum engineering efiiciency. Similarly, to facilitate fluid velocity and pressures changes inaccord with the techniques. of gas dynamics the cross-sectional area of the channel may increase or decrease and the shape may vary along the axis thereof. In general, the cross-sectional area may increase if acceleration is desired and may decrease if compression is desired. I

FIG. 2 shows. a simplified diagram of a plasma accelerator constructed in accordance with the teachings of this invention and placedin an accelerating systemto replace 'a conventional compressor in a closed cycle MHD generation system. In FIG. 2, a source of gaseous fluid60, such as the gas emerging from a regenerator, boiler, or other heat-exchanger 61 which removes heat from the working fluid of an MHD generator, serves as the fluid input to accelerator 62. The fluid passes to the plasma accelerator 62 having entrance andexit electrode pairs 63 and 64 circuit of the transverse electric currents generated by the interaction of the ionized fluid with the magnetic field. In operation, the accelerating fluid may pass to an ionizlng chamber 67 where the gas is ionized by any convenient means. The gas subsequently passes to the plasma accelerator 62 where a longitudinal velocity and/ or compression is imparted thereto. The fluid is then returned to the input heat exchanger 68 and thence to the MHD generator. It was noted previously, that the plasma accelerator of the present invention may be utilized to ionize as well as accelerate the gas; accordingly, the system of FIG. 2 may be altered to eliminate the ionizing chamber if ionization is accomplished by the acceleration-compressor itself as described above.

It will be obvious to those skilled in the art that many variations and modifications of the disclosed plasma accelerator may be made without departing from the spirit and scope of the invention, and therefore this invention is to be considered as limited only in accordance with the teachings thereof as set forth in the claims appended hereto.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method for accelerating or compressing an ionized fluid in a channel having a longitudinal axis comprising, establishing a magnetic field having lines of flux transverse to the longitudinal axis of said channel and passing through the ionized fluid in said channel, impressing a voltage on said fluid at spaced points along said channel to establish a longitudinal electric field in said channel cooperating with said magnetic field to produce a current component transverse to said lines of flux and to said electric field, and providing a completed electrical circuit externally of said fluid for said transverse current to flow in said fluid.

2. An ionized fluid accelerator-compressor comprising, means defining a channel for confining said fluid during its flow through said channel, means impressing a magnetomotive force transversely of said channel to produce at magnetic field in said channel having lines of flux transverse to the axis of said channel, longitudinally spaced mutually insulated electrode means, means impressing a voltage on said electrode means to establish a longitudinal electric field in said channel cooperating with said magnetic field to create a transverse electric current component in a direction transverse to said lines of flux and to said electric field, and means including additional electrode means oppositely located with respect to said channel for electrically connecting said transverse electric current to an electrical circuit completed externally of said fluid to cause a transverse electric current flow in said fluid.

3. An ionized fluid accelerator-compressor comprising, means defining a channel confining said fluid during its flow through said channel, means providing a magnetic field in said channel having lines of flux transverse to the axis of said channel, means for establishing a longitudinal electric field in said channel thereby creating a transverse electric current component in a direction transverse to said lines of flux and to said electric field, at least two electrodes placed in contact with said fluid intermediate the entrance and exit of said channel and positioned across the channel from each other in the direction of said transverse electric potential, and means for electrically connecting said electrodes to each other to cause a transverse electric current flow in said fluid.

4. An ionized fluid accelerator-compressor comprising, means defining a channel for confining said fluid during its flow through said channel, means providing a magnetic field in aid channel having lines of flux transverse to the axis of said channel, said channel including at least one electrode at the fluid entrance to said channel and at least one electrode at the fluid exit of said channel, a source of electric potential, means connecting said source of electric potential between said electrodes to establish a longitudinal electric field in said channel thereby creating a axis of said channel, said channel including at least one 7 electrode at the fluid entrance to said channel and at least one electrode at the fluid exit of said channel, a source of electric potential, means connecting said source of electric potential between said electrodes to establish a longitudinal electric field in said channel thereby creating a transverse electric current component in a direction transverse to said lines of flux and to said electric field, at least two electrodes placed in contact with said fluid intermediate the entrance and exit of said channel and positioned diametrically across the channel from each other in the direction of said transverse electric potential, and means for electrically connecting said last mentioned electrodes to each other to cause a transverse electric current flow in said fluid.

6. A gas accelerator-compressor comprising, means de fining a channel for confining said gas during its flow through said channel, means providing a magnetic field in said channel having lines of flux transverse to the axis of said channel, means for establishing a longitudinal electric field in said channel, said longitudinal electric field being of suflicient magnitude to cause ionization of said gas thereby creating a transverse electric current component in a direction transverse to said lines of flux and to said electric field, and means including contact means on Opposite sides of said channel and in contact with said gas for electrically connecting said transverse electric current to an electrical circuit completed externally of said gas to cause a transverse electric current to flow in said gas.

7. A gas accelerator-compressor comprising, means defining a channel for confining said gas during its flow through said channel, means providing a magnetic field in said channel having lines of flux transverse to the axis of said channel, means for'establishing a longitudinal electric field in said channel, said longitudinal electric field being of sufiicient magnitude to cause ionization of said gas thereby creating a transverse electric current component in a direction transverse to said lines of flux and to said electric field, at least two electrodes placed in contact with said gas intermediate the entrance and exit of said channel and positioned across the channel from each other in the direction of said transverse current component, and means for electrically connecting said electrodes to each other externally of said gas to cause a transverse electric current flow in said gas.

8. A gas accelerator-compressor comprising, means defining a channel confining said gas during its flow through said channel, means providing a magnetic field in said channel having lines of fiux transverse to the axis of said channel, said channel including at least one electrode at the gas entrance to said channel and at least one electrode at the gas exit of said channel, a source of electric potential of sufficient magnitude to cause ionization of said gas when connected to said electrodes, means connecting said source of electric potential between said electrodes to establish a longitudinal electric field in said channel thereby creating a transverse electric current component in'a direction transverse to said lines of flux and tosaid electric field, and means including electrode means positioned on opposite sides of said channel in contact with said gas for electrically connecting said transverse electric potential to an electrical circuit completed externally of said gas to cause a transverse electric current to fio-W in said gas. 7 7

9. A gas accelerator-compressor comprising, means providing a magnetic field in said channelhavinglines of flux transverse to the axis of said channel, said channel including at least one electrode at the gasjentrance of said channel and at least one electrode at the gas exit of said channel, a source of electric potential of sufficient magnitude to cause ionization of said gas when connected between said electrodes, means connecting said source of electric potential between said electrodes to establish a longitudinal electric field in said channel thereby creating a transverse electric current component in a direction transverse to said lines of flux and to said electric field, at

least two electrodes placed in contact with said gas intermediate the entrance and exit of said channel and positioned across the channel from each other in the direction of said transverse electric current, and means for electrically connecting said last mentioned electrodes to each other to causea transverse current flow in said gas.

electrode at the gas exit of said channel, a source of electric potential of sufiicient magnitude to cause ionization of said gas when connected between said electrodes, means connecting said source of'electric potential between said electrodes to establish a longitudinal electric field in said channel thereby creating a transverse electric mentioned electrodes to each other to cause a transverse 7 electric current fiow in said gas, said last named means including a source of potential poled in the direction to aid the flow of said-transverse electric current.

References Cited by the Examiner UNITED STATES PATENTS 2,217,187 10/40 Smith 313-161 2,880,337 3/59 Langmuir 31511,1X 2,927,232 a 3/60 Luce 313-161 X 2,971,122 2/61 Sloan 3l3161 X 3,091,709

' 5/63 Rosa 313111 X GEORGE N. 'WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

1. A METHOD FOR ACCELEATING OR COMPRESSING AN IONIZED FLUID IN A CHANNEL HAVING A LONGITUDINAL AXIS COMPRISING, ESTABLISHING A MAGNETIC FIELD HAVING LINES OF FLUX TRANSVERSE TO THE LONGITUDINAL AXIS OF SAID CHANNEL AND PASSING THROUGH THE IONIZED FLUID IN SAID CHANNEL IMPRESSING A VOLTAGE ON SAID FLUID AT SPACED POINTS ALONG SAID CHANNEL TO ESTABLISH A LONGITUDINAL ELECTRIC FIELD IN SAID CHANNEL COOPERATING WITH SAID MAGNETIC FIELD TO PRODUCE A CURRENT COMPONENT TRANSVERSE TO SAID LINES OF FLUX AND TO SAID ELECTRIC FIELD, AND PROVIDING A COMPLETED ELECTRICAL CIRCUIT EXTERNALLY OF SAID FLUID FOR SAID TRANVERSE CURRENT TO FLOW IN SAID FLUID. 